Means and method for achieving an optimum acid strength for an alkylation unit

ABSTRACT

A control system controls the acid strength of reaction acid in an alkylation unit reacting an olefin with an isoparaffin in the presence of the reaction acid to eventually produce an alkylate. The system senses the actual reaction acid strength, the discharge acid flow rate, the flow rate of discharge acid leaving the alkylation unit, the bottom products flow rate and the alkylate content of the bottoms product from a debutanizer tower and the propylene and butylene content of the olefin stream entering the alkylation unit. Using equations hereinafter disclosed, along with economic values associated with the acid and the alkylate, the control system periodically determines the optimum reaction acid strength. When the change in the reaction acid strength necessary to achieve the optimum reaction acid strength is less than a predetermined change, the necessary change is implemented. When the necessary change is greater than the predetermined change, the reaction acid strength is changed by an increment equal to the predetermined change. Where the reaction aicd strength is decreased to achieve an optimum reaction acid strength, a minimum limit is imposed on the reaction acid strength to prevent undesirable side reactions, such as olefin polymerization, from occurring.

United States Patent Hopkins et al.

[ Apr. 17, 1973 MEANS AND METHOD FOR ACHIEVING AN OPTIMUM ACID STRENGTH FOR AN ALKYLATION UNIT [75] Inventors: Walter L. Hopkins, Houston;

Donald E. Sweeney, Jr., Beaumont; Herbert J. Pitman, Nederland, all of Tex.

[73] Assignee: Texaco Inc., New York, N.Y.

[22] Filed: Feb. 24, 1972 [21] Appl. No.: 228,826

[52] U.S. C1. ..235/l5l.l2, 23/255 E, 208/D1G. l,

[51] Int. Cl. ..G06f 15/46, C07c 3/52 [58] Field of Search ..235/151.12, 150.];

23/230 R, 252 E, 232 E, 253 R, 254 E, 255 E; 260/6834, 683.43, 683.46, 683.59, 683.62; 208/133, 134, DIG. 1

[56] References Cited UNITED STATES PATENTS 3,002,818 10/1961 Berger ..235/l51.12

3,173,969 3/1965 Kapf ..260/683.59 X

3,325,391 6/1967 Waterman et al. .....260/683.43 X

3,442,972 5/1969 Massa ..260/683.62 X

3,513,220 5/1970 Brandel ..23/230 R X 3,625,655 12/1971 Culp et al. ..260/683.59 X

3,649,202 3/1972 Bajer et al. ..208/D1G. l

Primary Examiner--Joseph F. Ruggiero Att0rneyThomas H. Whaley et al.

[5 7 ABSTRACT A control system controls the acid strength of reaction acid in an alkylation unit reacting an olefin with an isoparaffin in the presence of the reaction acid to eventually produce an alkylate. The system senses the actual reaction acid strength, the discharge acid flow rate, the flow rate of discharge acid leaving the alkylation unit, the bottom products flow rate and the alkylate content of the bottoms product from a debutanizer tower and the propylene and butylene content of the olefin stream entering the alkylation unit. Using equations hereinafter disclosed, along with economic values associated with the acid and the alkylate, the control system periodically determines the optimum reaction acid strength. When the change in the reaction acid strength necessary to achieve the optimum reaction acid strength is less than a predetermined change, the necessary change is implemented. When the necessary change is greater than the predetermined change, the reaction acid strength is changed by an increment equal to the predetermined change. Where the reaction aicd strength is decreased to achieve an optimum reaction acid strength, a minimum limit is imposed on the reaction acid strength to prevent undesirable side reactions, such as olefin polymerization, from occurring.

14 Claims, 18 Drawing Figures TOP PRODUCTS 44 V oesgg g zzR E so 517 ALKYLATE HYDROCARBON MQRQ L SIGNAL E E ACID-HYMDIF)?(OCARBON PRODUCT IS I MEANS I5 A 17 i 43J I BOTTOM PRODUCTS INCLUDING V 42A ALKYLATE 57 8 ll v i l E I 0 2 E A B LEVEL ACID v RECORDER PROGRAMMER r 4 CONTROLLER SETTLER ACID 56 E2 J STRENGTH so L16 1, F SIGNAL FEEEIL, L E4 MEANS Cl K 17 ACID E 35 7 STRENGTH i i gg 7 ANALYZER 1 e24 CONTACTOR 25 u 42 4 L LEM E FLOW OPTIMUM RECORDER CONTROL 52 v CONTROLLER D G NR 1 SYSTEM L OLEFIN 40 X l 4/ E E SIGNAL s 24' 3o i MEANS DISCHARGE 12 ACID i 4| V5 M souRcE CHROMATOGRAF'H OF MEANS Dc 6 36 VOLTAGE v -v v g 7 2 OLEFIN 5 25 L P 38 AND ISOPARAFFIN MEANS AND METHOD FOR ACHIEVING AN OPTIMUM ACID STRENGTH FOR AN ALKYLATION UNIT BACKGROUND OF THE INVENTION present invention, control the reaction acid strength as a function of the deterioration or the anticipated deterioration of the reaction acid during the alkylation process. The reaction acid strength is maintained at a predetermined value.

The system and method of the present invention is completely different in concept from the aforementioned control systems. The present system and method controls the acid strength as a function of the economic values of the acid and the alkylate so that an optimum acid strength may be achieved. Furthermore, the present system and method may be used in conjunction with the control systems disclosed in the aforementioned applications to maintain the reaction acid strength at an optimum value.

SUMMARY OF THE INVENTION A system controls the strength of reaction acid in a reaction unit wherein an isoparaffin is reacted with an olefin in the presence of the reaction acid to provide an acid-hydrocarbon mixture to a settler where a hydrocarbon product is separated from the reaction acid and provided to a de-butanizer tower whose bottom products include alkylate; and a portion of the reaction acid is recycled while the remaining reaction acid is discharged from the alkylation unit; and wherein fresh acid is added to the recycle acid to affect the strength of the reaction acid. The circuit includes control apparatus which controls the reaction acid in accordance with a control signal. The flow rates of the reaction acid and the bottom products are sensed and corresponding signals provided. Signals corresponding to concentrations of different constituents of the olefin and of the alkylate in the bottom products stream are also provided. Apparatus senses the strength of the reaction acid and provides a signal representative of the acid strength. Signals corresponding to the economic values of acid and of octane of the alkylate are provided. The circuit provides the control signal in accordance with the signals corresponding to one of the acid flow rates, the alkylate flow rate, the concentration of the constituents of the olefin and of the alkylate, the acid strength of the reaction acid and the economic values of the acid and the octane rating to achieve an optimum acid strength for the reaction acid.

The objects and advantages of the invention will appear more fully hereinafter from a consideration of the detailed description which follows, taken together with the accompanying drawings wherein one embodiment of the invention is illustrated by way of example. It is to be expressly understood, however, that the drawings are for illustration purposes only and are not to be construed as defining the limits of the invention.

DESCRIPTION OF THE DRAWINGS FIG. 1 shows a simplified block diagram of a system for controlling the strength of reaction acid in an alkylation unit which is also shown in partial schematic form.

FIG. 2, comprising FIGS. 2A-2G, is a diagrammatic representation of pulses occurring during the operation of the system shown in FIG. I

FIGS. 3 and 4 are detailed block diagrams of the programmer and the acid strength signal means, respectively, shown in FIG. 1.

FIG. 5 is a detailed block diagram of the olefin signal means shown in FIG. 1.

FIG. 6 is a detailed block diagram of the optimum control system shown in FIG. I, constructed in accordance with the present invention.

FIGS. 7 through 10 are detailed block diagrams of the 0 computer, the at computer, the p computer, and the R and S computer shown in FIG. 6. FIGS. 11A and 11B, when matched along matching line AA, is a detailed block diagram of the control means in FIG. 6.

DESCRIPTION OF THE INVENTION Referring to FIG. 1, there is shown a portion of an alkylation unit in which an olefin is reacted with isoparaffin in the presence of a catalyst, such as sulfuric or hydrofluoric acid and which is hereinafter referred to as the reaction acid, to form a higher molecular weight isoparaff'm. For purpose of explanation, the acid in the following description shall be sulfuric acid. The olefin may be butylenes, propylene or a mixture of butylenes and propylene, while the isoparaff'm may be isobutane. The control system shown in FIG. 1 controls the strength of the reaction acid during the reaction by determining the actual reaction acid strength to achieve an optimum strength.

The olefin and isoparaffin enter a contactor 4, by way of a line 6, where the olefin and isoparaffin are contacted with the reaction acid entering by way of a line 7. Contactor 4 provides an acid-hydrocarbon mix by way of a line 8 to an acid settler 12. Settler l2 separates the hydrocarbon product from the reaction acid and the hydrocarbon product is provided to a debutanizer tower 13 through a line 14 while the reaction acid is removed by way of a line 16. Acid settler 12 may be the only acid settler in the unit or it may be the last acid settler of a group of acid settlers. A top products stream leaves tower 13 by way of a line I]. while a bottom products stream, which includes alkylate, leaves tower 13 by way of a line 15. Fresh acid enters line 16 by way of a line 17 as needed to maintain a desired reaction acid strength. A pump 20 pumps the reaction acid from line 16 into line 7. A portion of the reaction acid in line 7 is discharged by way of a line 21. The discharge acid may be provided to another alkylation unit or disposed of.

An acid strength analyzer 22 periodically samples the acid in line 16 and provides signals E through E.

Acid strength analyzer 22 may be of the type fully disof the acid in line 16 is controlled by a signal E, from a programmer 27, as hereinafter described. Signal E shown in FIG. 2A, from analyzer 22 occurs at the time at which titration is initiated, while signal E shown in FIG. 28, occurs at the time at which titration is completed. The occurrence of pulse signal E indicates that the amplitude of signal E corresponds to the density of the acid sample. Signals E, E, from analyzer 22 are applied to programmer 27, while signals E E, are applied to acid strength signal means 35, which is hereinafter described in detail.

Programmer 27 controls the development of a signal E corresponding to an optimum flow rate of discharge acid. The quantity of fresh acid entering the alkylation unit is controlled by controlling the'quantity of acid being discharged to control the strength of the reaction acid. Programmer 27 which is described in detail hereinafter, receives a pulse signal E, from chromatograph means 36. Chromatograph means 36 samples the stream in line 6 and provides signals E, and E The peaks of signal E correspond to concentrations of different constituents of the stream in line 6. Each pulse in pulse signal E, coincides with a different peak of signal E Programmer 27 provides a signal E corresponding to the titration time of the reaction acid sample with a caustic, a reset pulse E and control pulses E B, through E Signal E and control pulses E,,, E, are applied to acid strength signal means 35 which also receive direct current voltages V through V, from a source of direct current voltages 38.

Acid strength signal means 35, which is described in detail hereinafter, provides a signal E corresponding to the strength of the reaction acid, to an optimum control system 40. For convenience, the term acid strength shall hereinafter be used in lieu of reaction acid strength whether said strength is an actual strength, a predicted strength or a reference strength. Control system 40, which is described in detail hereinafter, determines the optimum acid strength and provides a signal E corresponding to a target flow rate for the discharge acid to achieve an optimum acid strength. Control system 40 receives direct current voltages V; through V and V from source 38 and a signal E from olefin signal means 41 corresponding to the ratio M of propylene in line 6 to the olefins in line 6. Control system 40 also receives a signal E from a sensor 42 in line 21 representative of the flow rate of the discharge acid which is substantially equal to the flow rate of the fresh acid in line 17, and a signal E corresponding to the bottom products flow rate, from a sensor 42A in line 15.

Olefin signal means 41 provides signal 15,, in accordance with signal E from chromatograph means 36 and control pulses E through E and E from programmer 27.

Chromatograph means 43 samples the bottom products stream in line 15 to provide a pulse signal E to programmer 27 and a signal E to alkylate signal means 44 receiving direct current voltages V through V from direct current voltage source 38 and pulses E0, Ep, Ea, ER, Es, E1, EU, Ev, Ew, Ex, Ey, Ez from programmer 27. The peaks of signal E correspond to concentrations of different constituents of the bottom products. Each pulse in pulse signal E coincides with a different peak of signal E Alkylate signal means 44 is controlled by pulse signals E through E from programmer 27 to provide a signal E to optimum control system 40 corresponding to the concentration of alkylate in the bottom products stream in line 15.

Alkylate signal means 44 is similar to the olefin signal means described in the aforementioned U.S. application Ser. No. 169,443 except that signal E corresponds to the normalized constituent with six or more carbon atoms. Olefin signal means 41 is also similar to dividing the held peak of signal E corresponding to the concentration of compounds with six or more carbon atoms to provide signal E Signal E is applied to a conventional type flow recorder controller 50 receiving signal E from flow ratesensor 42 and providing a signal to a valve 52 in line 21 to control the flow rate of the discharge acid.

The flow rate of the fresh acid in line 17 is controlled as a function of the discharge acid flow rate to affect the acid strength. When the discharge acid flow rate is increased, the acid level in acid settler 12 decreases. A level sensor 56 senses the acid level in settler 12 and provides a corresponding signal to a conventional type level recorder controller 57. Controller 57, whose preset set point corresponds to a predetermined acid level for settler 12, provides a signal, corresponding to the difference between the set point acid level and the settler 12 acid level, to a valve 60 in line 17 to increase the fresh acid flow rate thereby restoring the acid level in acid settler 12 to the predetermined level and increasing the acid strength. When the discharge acid flow rate is decreased, the acid level in settler 12 increases causing a decrease in the fresh acid flow rate and a decrease in acid strength.

Reset pulse E developed in programmer 27 resets circuits in acid strength analyzer 22, programmer 27, chromatograph means 36, optimum control system 40 and chromatograph means 43.

Referring to FIG. 3, programmer 27 includes a conventional type on-off switch 101 which receives a direct current voltage V from source 38. Switch 101 controls the operation of control system 40. When activated, switch 101 passes voltage V to operate clock means 105. Clock means 105 periodically provides a reset pulse E The pulse repetition rate of pulses B, should be of sufficient duration to allow the alkylation unit to stabilize.

Pulse signal E, from chromatograph means 36 is applied to an AND gate 106 which controls the development of pulse signals E through E,;. AND gate 106 is enabled by a high level direct current output from a logic decoder 108. When enabled, pulse signal E, passes through AND gate 106 into a conventional counter which counts the pulses in signal E, coinciding with different peaks in signal E Logic decoder 108 decodes the count in counter 110 to provide a plurality of outputs to monostable multivibrator 114.

Logic decoder 108 may be of the type that includes AND gates connected to each stage of counter 110 in a manner so that each AND gate provides an output for predetermined counts in counter 110. Upon reaching a count of 10, the direct current output provided by logic decoder 108 to AND gate 106 goes to a low level thereby disabling AND gate 106 to block pulse signal E to prevent further counting by counter 110.

Monostable multivibrators 114 represent a plurality of monostable multivibrator, each monostable multivibrator is connected to a different AND gate in decoder 108 and is triggered by its output to provide a pulse. Monostable multivibrators 114 provide a plurality of control pulses E through E which coincide with certain peaks of signal E corresponding to the various olefin constituents of the stream in line 6 as determined by chromatograph means 36. FIG. 2C shows pulse E while FIG. 2D shows pulse E It should be noted that there is only one break associated with pulse E This is because pulse E preceded pulse E in time and in this particular example, pulse E is used to start the timing sequence and is therefore time related to the pulses shown in FIGS. 2F and 2G.

Pulse E from monostable multivibrators 114 triggers yet another monostable multivibrator 116 which acts as a time delay and provides a pulse to a flip-flop 117. The trailing edge of the pulse E; from multivibrator l 16 triggers flip-flop 117 to its set state. The output of a flip-flop is a high level direct current voltage, when the flip-flop is in a set state and a low level direct current voltage when the flip-flop is in a clear state. Flipflop 117 provides its output as signal E shown in FIG. 2B, to acid strength signal means 35 and to an AND gate 118 partially enabling AND gate 118.

The end of titration signal E triggers a flip-flop 132 to a set state causing flip-flop 132 to provide a high level direct current output to AND gate 118. AND gate 118 controls the development of pulse signals E and E so that they only occur after the acid strength analysis and the olefin and isoparaffin stream analysis have been completed. When fully enabled, AND gae 118 passes timing pulses from a clock 120 to a conventional counter 124. A logic decoder 125 decodes the count in counter 124 to provide two trigger outputs, at different times, to two monostable multivibrators shown, as monostable multivibrators 127. Monostable multivibrators 127 provides signals E and E; as shown in FIGS. 2F and 2G, respectively.

The titration time signal E is developed by a flip-flop 140, a clock 141, AND gate 142, monostable multivibrators 144 and 145, a counter 148, a storage register 150 and a digital-to-analog converter 151. The start of titration signal 5, from acid strength analyzer 22 triggers flip-flop 140 to a set state. The high level output from flip-flop 140 enables AND gate 142 causing it to pass timing pulses to counter 148. Counter 148 counts the timing pulses passed by AND gate 142. The

end of titration signal E triggers flip-flop 140 to a clear state. The resulting low level output from flip-flop 140 disables AND gate 142. When disabled, AND gate 142 blocks the timing pulses from clock 141 so that the count in counter 148 corresponds to the time interval between signals E E which is the titration time.

The change in the output from flip-flop 140 from a high level to a low level triggers multivibrator 144 causing it to provide a time delay pulse. The trailing edge of the pulse from multivibrator 144 triggers multivibrator so that multivibrator 145 provides a pulse after counter 148 has completed a count. The pulse from multivibrator 145 controls storage register to accept and store the count from counter 148. Digital-toanalog converter 151 converts the count stored in register 150 to signal E AND gates 106A, receiving signal E and 118A; counters 110A and 124A; logic decoders 108A and 125A; and monostable multivibrators 114A and 127A cooperate in a manner similar to the cooperation of AND gate 106, counter 110, logic decoder 108 & monostable multivibrators 114 to provide pulses E through E Pulses E through E coincide with different peaks of signal E which corresponds to the concentration of alkylate in the bottom products. Pulses Ey, E are sampling pulses which control sample and hold circuits.

Reset pulse E resets counters 110, 110A, 124, 124A and 148, flip-flops 117, 117A and 132 and storage register 150.

Referring to FIG. 4, acid strength signal means 35 provides signal E corresponding to the acidstrength A in accordance with the following equations:

where VOL is the volume of caustic required by the titration of the acid sample, N is the normality of the caustic, MEQ is milliequivalent weight of the acid, and W is the weight of the acid. Equation 1 may be rewritten as:

1=[( c) e) (MEQA)/(DA) 8) where AT is the titration time, FR, is the flow rate of the caustic, D is the density of the acid and VOL, is the volume of the acid sample.

Acid strength signal means 35 includes sample and hold circuits 160, 161, multipliers 162 through 162C, a divider 163 and an electronic switch 164. Signal E, from analyzer 22, which occurs when signal 13., corresponds to the density D A of the acid sample, controls sample and hold circuit to sample and hold signal E The output of sample and hold circuit 160 is applied to multipler 162 where it is multiplied with direct current voltage V which corresponds to the volume VOL, of the acid sample. Multipler 162 provides a signal corresponding to the denominator in equation 2. Y

Multiplier 162A multiplies the titration time signal E from programmer 27 with voltage V., from source 38, which corresponds to the caustic flow rate to provide a product signal corresponding to (AT) (FR The product signal from multiplier 162A is multiplied with voltage V corresponding to the normality of the caustic, which by way of example, may be 0.2 meq/rnl, by multiplier 16213 to provide a product signal to multiplier 162C whereit is multiplied with direct current voltage V Voltage V corresponds to the milliequivalent weight MEQ of the acid which for purpose of illustration may be sulphuric acid H 80 whose milliequivalent weight is 0.04904 gram/meq.

The product signal from multiplier 162C corresponds to the numerator in equation 2. Divider 163 divides the numerator signal from multiplier 162C with the denominator signal from multiplier 162 to provide a signal, which corresponds to the sensed acid strength A to electronic switch 164. Electronic swith 164 is controlled by pulse signal B, so as to pass the acid strength signal from divider 163. Sample and hold circuit 161 is controlled by pulse E, from programmer 27 to hold the A signal passed by switch 164 to provide signal E corresponding to the acid strength A Olefin signal means 41 provides a ratio M signal E which is used to determine an octane adder factor as hereinafter explained, in accordance with the following equation:

3. M (propylene/olefins) X 100% Referring to FIG. 5, the peaks of signal E from chromatograph means 36 correspond to the concentrations of different constituents of the charge olefin and isoparaffin in line 6. Sample and hold circuits 170 through 170C are conrolled by pulse signals E through E; to hold some of the different peaks of signal E The following table relates a particular sample and hold circuit to a corresponding olefin constituent of the stream in line 6.

CIRCUIT CONSTITUENT 170 Propylene 170A Butylenes 170B Pentylenes 170C All olefinic compounds with six or more carbon atoms The outputs from sample and hold circuits 170 through 170C are applied to multipliers 171 through 171C where they are multiplied with voltages V through V corresponding to scaling factors pertaining to the particular constituents. By way of example, the voltages V, through V may correspond to 0.2, 0.10, 0.02 and 0.10, respectively. The product signals from multipliers 171 through 171C are sampled and held by circuits 172 through 172C, respectively, in response to pulse signal E from programmer 27. Sample and hold circuits 172 through 172C are used so that outputs corresponding to the various olefin concentrations of the charge olefin and isoparaffin in line 6 may be presented simultaneously to summing means 175. Summing means 175 provides a signal corresponding to the denominator of equation 3.

A divider divides the output from sample and hold circuit 172, which corresponds to the numerator of equation 3, with the sum signal from summing means 175 to provide the ratio M signal E It has been determined from empirical data that there exists an economic relationship between the octane rating of the alkylate provided by an alkylation unit and the strength of the reaction acid in the alkylation unit. Further, if the alkylate production rate is maintained at a constant value then the profit of the al- .kylation unit will vary as a function of theacid strength.

An equation may be formulated to describe the akylation units profit. The profit equation may be a second order equation such as Equation 4 or a linear equation such as Equation 5.

5. p Q RA where p is the differential profit, Q, R and S are constants and A is acid strength.

For the situation where Equation 4 describes the alkylation unit's profit, a first and second derivative of Equation 4 may be taken to yield equations 6 and 7.

6. dp/dA R 28A and 7. a p/dA 28 8. A R/2S When S is not 0, the maximum or minimum point of a curve described by Equation 4 can be determined by setting Equation 6 equal to 0 and solving for .A as shown in Equation 8. When S is negative, the point is a maximum point and Equation 4 is used to control the alkylation unit. When S is positive the point is a minimum point. When S is positive or substantially equal to zero, equation 5' is used to control the alkylation unit. The values for S and R can be determined by increasing the acid strength by a predetermined amount to a value A and decreasing the acid strength by a predetermined amount to a value A and rewriting Equation 4 for the three acid strength conditions.

9- [42 14 +A, and

10. A3 A1 -A where A is the predetermined acid strength change and by way of example may be 0.1 weight percent.

The profit differentials p,, p, and p may be determined by subtracting the present profit position P from the profit positions P P, and P The profit positions equations for P P and P are as follows:

a (3) (4 3) 4) where AR AR, and AR; are acid rates for acid strength A,, A and A respectively, in tons per day, V and V, are predetermined economic values for the acid and octane rating of the alkylate, ALR is the alkylate production rate in barrels per day, da b, and b, are octane adder factors for acid strengths A A, and A respectively and k represents constant production costs. Thus, p, is zero, while p and p are described by equations 17 and 18.

The octane adder may be written in general form dM oo) A wl where K through K, are factors associated with a particular alkylation unit for a particular acid strength and a particular M ratio, which may have the following values:

Factor M M Y MZM K, 0.51 15 0.0

where M is 35 percent and M is 60 percent.

From the factor table we may write the following equations for 4 which is used when M is equal to or less than 35 percent, di for use when M isequal to or greater than 60 percent and for use when M is greater than 35 percent but less than 60 percent.

20. da 0.51 15(AA, 0.05582(AA,,)*+

values of 7.7112

22. (My: d

The acid rate AR, and the alkylate rate AL-R are obtained by converting the flow rates of the reaction acid and the alkylate in the bottom products, respectively, from barrels per hour to tons per day and to barrels per day, respectively, in accordance with equations 23 and 24.

23. AR,= (H) (FR,,)

24. ALR= (FR (J) (ALK) where FR and FR are the flow rates of the reaction acid and the bottom products, respectively, H and J are conversion factors which by way of example may have hr-ton/day-bbl and 24 hrs/day, respectively, and ALK is the concentration of alkylate in line 15. Acid rates AR and AR, for increased and decreased, respectively, acid strength conditions can be determined from equations 25. AR /0,) AR, and

26. AR,,= (6 /0,) AR,

The general equation for an acid multiplier is j( 90) k( 90) where K are factors associated with a particular alkylation unit and acid strength condition. By way of example for an acid strength equal to or greater than 90 weight percent: K, =1.0, K, 0.03686 and K 0.02454 while K,, K, and K are equal to 0.0. Therefore equation 27 may be rewritten as:

The multipliers 0,, 6 and 6,, are determined from equation 28 by substituting A,, A and A respectively, for A.

Equations 29 through 31 are as follows:

D 1( 2 3 2( 1 3( 1 2 However, since p, is zero, equations 29 and 30 may be rewritten as R [1 2( a 1 +P3( 1 2 )l/ and 33. S [p (A, A +P3(Az A1)]/D, respectively.

The values for R and S may be inserted in equation 8 to determine the optimum acid strength A,,.

When controlling the acid strength to achieve an optimum value, it is highly desirable that the change in the acid strength should not exceed the predetermined amount A. When required change to achieve the optimum acid strength is greater than A, the acid strength is changed by the amount A.

In controlling the acid strength to achieve an optimum strength the acid strength should not be allowed to drop below 90 weight percent so as to prevent undesirable side reactions, such as olefin polymerization from occurring.

When it has been determined that S is positive or zero, equation 5 is used to control the acid strength. Since equation 5 is a linear equation, differential profit points p,, p and p lie along a straight line. However, it is not known which point, p or p;,, offers the greater profit. Differential profit points p and p are compared with each other. When 2,, is greater than 11 the reaction acid strength is increased by the amount A. When p, is greater than p the reaction acid strength is decreased by the amount A.

Referring now to FIG. 6, optimum control system 40 includes a 6 computer 200 which receives signal E,, correspoinding to the sensed acid strength, and direct current voltages V through V,,. Computer 200 provides a signal E corresponding to the term 0, in accordance with equation 28. Voltage V corresponds to A while voltages V -V correspond to the factors 1.0, 0.03686 and 0.02454 in equation 28, respectively. Referring also to FIG. 7, subtracting means 201 in computer 200 subtracts voltage V from signal E,, to provide an output corresponding to the term (A,A A multipliers 202 effectively squares the output from subtracting means 201 while another multiplier 203 multiplies the output from subtracting means 201 with voltage V The output from multiplier 202 is multiplied with voltage V,, by a multiplier 207. Summing means 208 sums voltage V with the outputs from multipliers 203, 207 to provide signal E Direct current voltage V corresponds to the predetermined change A for the acid strength. Summing means 212 in FIG. 6 sums signal E, with voltage V,,, to provide a signal E,, corresponding to the increased acid strength A Similarly subtracting means 213 subtracts voltage V,,, from signal E,, to provide a signal E,, corresponding to the reduced acid strength A Signals E,,,,, E,,,, are applied to 0 computers 2(DA and 200B, respectively. Elements having a number with a suffix are connected and operate in a similar manner to elements having the same number without a suffix. Computers 200A, 200B also received direct current voltages \1 through V,, to provide 6 signal E and 0 signal E respectively. A pair of dividers 215, 216 divide signals E and E respectively, with signal E to provide signals E and E respectively, corresponding to the terms 0 /0, and 0 /0, respectively, in equations 25 and 26.

The reaction acid flow rate signal E,, is multiplied with direct current voltage V,,, which corresponds to the conversion factor II in equation 23 for converting the flow rate from barrels per hour to tons per day, by a multiplier 217. Muliplier 217 provides a signal E corresponding to the acid rate AR, associated with sensed acid strength A,. A multiplier 220 multiplies signal E,, from divider 215 and E together to provide a signal E corresponding to acid rate AR which is associated with acid strength A Another multiplier 221 multiplies signals E and E together to provide a signal E corresponding to acid rate AR, which is associated with acid strength A Signal 13, corresponding to the bottom products flow rate is multiplied with signal E,-,, corresponding to the alkylate concentration in line 15 by a multiplier 223. The output from multiplier 223 is multiplied with voltage V, by a multiplier 224 to provide a signal E corresponding to the alkylate rate ALR. Voltage V, corresponds to the conversion factor J in equation 24.

Signal 15, from olefin signal means 41 is applied to a 4: computer 225 along with signal E,, and direct current voltages V and V, through V Referring now to FIG. 8, voltage V is again subtracted from signal E,, to

responding to the term 0.05582 in equation 20. A multiplier 231 multiplies the output from subtracting means 226 with voltage V corresponding to the term 0.5l 15. The output from subtracting means 226 is effectively raised to the fifth power by a logarithmic amplifier 234. The output from amplifier 234 is multiplied with a voltage V corresponding to the exponent 5, by a multiplier 235. An antilog circuit 236 which may be an operational amplifier having a function generator, of the typemanufactured by Electronics Associates as their part number PC-l2, as a feedback network provides a signal corresponding to the term (A -A in equation 20. A multiplier 240 multiplies the output from circuit 236 with voltage V corresponding to the term 0.00001363 in equation 20. Summing means 241 sums the outputs from multiplier 231, 240 to provide a signal to subtracting means 242. Subtracting means 242 subtracts the output by multiplier 230 from the output provided by summing means 241 to provide a signal E corresponding to the term 41 Similarly, an amplifier 234A, a-multiplier 235A, an antilog circuit 236A cooperate to provide a signal corresponding to (A -A using voltage V corresponding to the exponent 3. Amplifier 243 having unity gain inverts the signal from curcuit 236A to provide a signal which is multiplied with a voltage V corresponding to the term 0.003609 in equation 21, by a multiplier 244 to provide a signal E which corresponds to the term 4%.-

Voltages V,,,, V correspond to the ratios M L and M in equation 22, which for the particular alkylation unit have been selected at 35 percent and 60 percent, respectively. Subtracting means 247, 246 subtract voltage V from signal E and signal E from voltage V respectively, to provide outputs corresponding to the term (M-M,,) and (M -M), respectively, to dividers 251 and 250, respectively. Voltage V is subtracted from voltage V by subtracting means 248 to provide a signal corresponding to M M in equation 22. Dividers 250, 251 divide the outputs from subtracting means 246, 247 by the signal from subtracting means 248 to provide outputs to multipliers 252 and 253, respectively. Multiplier 252 multiplies the output from divider 250 with signal E while multiplier 253 multiplies the output from the divider 251 with signal E Summing means 254 sums the outputs from multipliers 252, 253 to provide a signal E corresponding to the term 4),, in equation 22.

Signals E E and E are applied to electronic switches 257, 257A and 2578, respectively, which are controlled to select one of the signals E E or B to be used as signal E Comparators 258, 259 compare signal E with voltages V and V respectively. Comparator 258 provides a high level direct current output when signal E is equal to or more negative than voltage V and a low level output when signal E is more positive than voltage V Comparator 259 provides a high level direct current output when signal E is greater than voltage V and a low level output when signal E is equal to or less than voltage V AND gates 260, 260A and 2608 control switches 257, 257A and 257 B.

When the M is less than M comparators 258, 259 provide a high level output and a low level output,

respectively. Inverters 261 262 invert the outputs from comparators 259 and 258, respectively, so that AND gate 260 provides a high level direct current output while AND gates 260A, and 2608 provide low level outputs. An electronic switch is rendered conductive by a high level direct current voltage and non-conductive by a low level direct current voltage so that switch 257 is rendered conductive by the output from AND gate 260. When signal E is less than voltages V and V switch 257 passes signal E while switches 257A and 257B block signals E and E respectively.

When signal E is greater than voltages V and V M is greater than M and comparators 258, 259 provide a low level output and high level output, respectively. Switch 257A is rendered conductive by the high level output from AND gate 260A receiving high level outputs from comparator 259 and inverter 262, to pass signal E AND gates 260, 2608 are disabled by low level outputs from comparator 258 and inverter 261,

respectively, thereby causing switches 257 and 257B to block signals E and E respectively.

When M is greater than M but less than M signal E is greater than voltage V and less than voltage V causing comparators 258, 259 to provide high level outputs. AND gate 260B provides a high level output in response to high level outputs from comparators 258, 259 while AND gates 260, 260A provide low level outputs in response to the low outputs from inverters 261 and 262, respectively. Switch 2578 passed signal E5; in response to the high level output from AND gate 260B, while switches 257, 257A block signals E and E respectively, in response to the low level outputs from AND gate 260 and 260A, respectively.

Similarly, 4) computers 225A, 2258 receive all of the signals and voltages that computer 225 receives with the exception that computers 225A, 225B receive signals E and E respectively, in lieu of signal E to provide signals E and E corresponding to 4:, and respectively, of equationsv 15, 17 and 16, 18, respectively.

It is necessary to compute the profits for the increased and decreased acid strengths A, and A conditions. Referring to FIG. 6, a p, computer 265 provides a signal E corresponding to the term p, in .equations 15, 17, 29, 30, 32 and 33 in accordance with signals E E E E and E and voltages V V Referring to FIG. 9, subtracting means 266 subtracts signal E from signal E to provide an output, which corresponds to the term (AR AR in equation 17, to a multiplier 267. Multiplier 167 multiplies the output from subtracting means 266 with voltage V which corresponds to the term V in equation 17. Subtracting means 269 subtracts signal E from signal E to provide a signal corresponding to the term .in equation 17, to a multiplier 270. A multiplier 271 multiplies voltage V which corresponds to the term V,,, and signal E 'together to provide an output to multiplier 270. Multiplier 270 multiplies the outputs from subtracting means 269 and multiplier 271 to provide a signal corresponding to the product (ALR) (V Summing means 272 sums the outputs from multipliers 267, 270 to provide signal E A computer 265A operates in a similar manner to provide signal E which corresponds to the term p in equations 18, 29, 30, 32, and 33 except that signals E E are used in lieu of signals E and E respectively.

Referring to FIGS. 6 and 10, an R and S computer 275 solves equations 31, 32 and 33 to provide signals E E corresponding to the terms R and S, respectively, in accordance with signals E E E113, E and E Signal E is subtracted from signal E by subtracting means 276, to provide a signal corresponding to the term (A A in equation 33. The signal from subtracting means 276 is multiplied by signal E by a multiplier 277 to provide a signal corresponding to the term p (A A in equation 33. Subtracting means 280 subtracts signal E from signal E to provide a signal, corresponding to the term (A -A in equation 33, which is multiplied with signal E by a multiplier 281 to provide a signal corresponding to p (A,--A Summing means 282 sums the signals from multipliers 277, 281 to provide a signal corresponding to the numerator of equation 33.

Multipliers 283, 284 and 285 effectively square signals E E and E respectively, to provide signals corresponding to A A and A}, respectively. Subtracting means 288 subtracts the output provided by multiplier 284 from the output provided by multiplier 283 to provide a signal corresponding to the term (AF-A in equations 29, 31 and 32. A multiplier 289 multiplies the output from the subtracting means 288 with signal E to provide a signal corresponding to A (A A in equation 31. Subtracting means 290 subtracts the output provided by multiplier 285 from the output provided by multiplier 284 to provide a signal corresponding to the term (A A in equations 31, 32. The output from subtracting means 290 is multiplied with signal E by a multiplier 291 to provide a signal which corresponds to the term A (A A in equation 3 l. Subtracting means 294 subtracts the output provided by multiplier 283 from the output provided by multiplier 285 to provide a signal corresponding to the term (Ag-A in equations 31, 32. A multiplier 295 multiplies the output from subtracting means 294 with signals E to provide a signal 'cor responding to the term A (A- A in equation 31. The outputs of multipliers 289, 291 and 295 are summed by summing means 296 to provide a signal corresponding to the term D in equations 29 through 33. A divider 297 divides the output from summing means 282 with the output from summing means 296 to provide signal E The output from subtracting means 288, 294 is multiplied with signals E and E respectively, by multipliers 299 and 300, respectively, to provide signals corresponding to the terms MAE-A and p (A;, -A, respectively, in equation 32. The signals from multipliers 299, 300 are summed by summing means 301 to provide a signal corresponding to the numerator in equation 32. The signal from summing means 301 is divided by the signal from summing means 296 by a divider 302 to provide signal E Referring to FIGS. 6 and 1 1, control means 305 provides signal E in accordance with signals E E E E E E and E and voltages V V V V and V A comparator 302 determines whether equation 4 or will control the acid strength by c omring signal E02 to a zero reference, s tichfigroimd 301. Equation 4 is used in controlling the alkylation unit when signal Em has a negative value, while equation 5 is used when signal E is positive or substantially zero. When Signal B62 is positive or equal to zero, comparator 302 provides a low level direct current signal E55.

Comparator 302 provides a high level output when signal E is negative. Thus, equation 4 will control when signal E is at a high level while equation 5 will control when signal E is at a low level as hereinafter explained.

SECOND ORDER EQUATION CONTROL A multiplier 310, a divider 311 and an inverting amplifier 312, having unit gain, comprise a computer for solving equation 8 for A the optimum reaction acid strength, and providing a signal E corresponding thereto. Multiplier 310 multiplies signal E with voltage V corresponding to the term 2S. Divider 311 divides signal E, with the signal from multiplier 310 to provide a signal corresponding to R/2S, which is inverted by amplifier 312 to provide signal E Subtracting means 313 subtracts the acid strength signal E from signal E to provide a signal E Signal E corresponds to the required change in the reaction acid strength to achieve the optimum reaction acid strength. However, as stated previously, the change in the reaction acid strength must not exceed the predetermined constraint value A. When the required change is greater than A, it is necessary that the acid strength be changed in the direction indicated by the required change but by the amount A. Since signal E may be a negative or positive direct current signal, an absolute value signal B is derived from signal E by the cooperation of multipliers 2358 and 316, a logarithmic amplifier 2343 and an anti-log circuit 236B. Multiplier 316 effectively squares signal E while logarithmic amplifier 234B, multiplier 235, receiving direct current voltage V corresponding to a value of 0.5 and anti-log circuit 236B obtain the square root of the signal from multiplier 316 to provide signal E A comparator 320 determines whether or not the required change to achieve the optimum reaction acid strength is greater than the constraint change A. Comparator 320 compares absolute value signal E withvoltage V corresponding to constraint change A, to provide a direct current signal E Signal B is at a high level when signal E is greater than voltage V and at a low level when signal E is equal to or less than voltage V Comparator 320 controls an electronic switch 323 to pass or block signal E so that signal E may be used in changing the system acid strength when the required change does not esceed the constraint change A. An inverter 321 inverts signal E so that when signal E is at a low level, inverter 321 provides a high level output to an electronic switch 323 rendering switch 323 conductive to pass signal E If other conditions, as hereinafter described, are met, signal E will be used to develop signal E When the required change to achieve the optimum acid strength is greater than the constraint change A, the acid strength is changed by the amount A. Inverted signal E from inverter 321 changes to a low level causing switch 323 to block signal B so that signal E cannot affect the acid strength. However, the change to the acid strength by the amount A must be in the direction determined by the polarity of signal E It is obvious that if the absolute value of signal E is greater than zero, then signal E will be some value other than zero.

Comparators 328, 329 compare signal E with a zero reference, which may be ground 301, to determine the polarity of signal E Comparators 328, 329 provide signals to AND gates 330 and 331, respectively. AND gates 330 and 331, OR gates 332 and 333, control electronic switches 336 and 337. Switch 336 receives voltage V while switch 337 receives an inverted voltage V corresponding to a-A from an inverting amplifier 334 receiving voltage V AND gates 330, 331 are controlled by signal E and by comparators 328 and 329, respectively. Thus AND gates 330, 331 are enabled by signal E which is at a high level, since the control of the alkylationunit by the second order equation is being described. When signal E is positive, comparators 328, 329 provide a high level signal and a low level signal,respectively. AND gate 330 provides a high level signal to switch 336 in response to high level signals applied to AND gate 330 causing switch 336 to pass voltage V to an electronic switch 338. Switch 338 allows the acid strength to be changed by the amount A when rendered conductive. Switch 338 is rendered conductive when the optimum acid strength is greater than A. An AND gate 342 receiving signals E and E renders switch 338 conductive when signals E and E are at high levels and non-conductive when signal E or E is at a low level.

An electronic switch 339 passes the passed signal from switch 323 or 338 when the profit equation is a second order equation so that the alkylation unit is controlled in accordance with equation 4 and blocks the passed signal from switch 323 or 338 when the profit equation is linear so that the alkylation unit is not con trolled in accordance with equation 4. Since the second order equation operation is being described, signal E is at a high level rendering switch 339 conductive to pass a signal from switch 323 or 338.

Summing means 345 sums the passed signal from switch 338 with voltage E to provide a signal E corresponding to a new target acid strength. A comparator 346 determines whether the new target acid strength is equal to or greater than A to prevent undesirable side reactions such as olefin polymerization. Comparator 346 compares signal E with voltage V corresponding to A to control an electronic switch 347, receiving voltage V, and signal E When the new target acid strength is less than the minimum allowable acid strength A switch 347 is controlled by the output from comparator 346 to pass voltage V, and block signal E When the new target acid strength is equal to or greater than voltage V electronic switch 347 is controlled by the output from comparator 346 to pass signal E from summing means 345 and to block voltage V,. The signal or voltage passed by switch 347 determines the acid strength for the alkylation unit.

Signal E or voltage V,,, whichever is passed by switch 347, is converted to signal E corresponding to the discharge acid flow rate by a computer 200C, dividers 350 and 351, and a multiplier 352. Computer 200C operates in a manner similar to the operation of computer 200, heretofore described in detail, except that signal E or voltage V, is used in lieu of signal E and computer 200C provides a signal E which corresponds to the new acid strength A instead of signal E Signal E is divided by signal E by divider 350 to provide a signal corresponding to O IO The signal from divider 350 is multiplied with signal E by multiplier 35210 provide a signal corresponding to the new acid rate AR Divider 351 provides signal E by dividing the AR signal with voltage V When signal E is negative, comparators 328, 329 provide a low level output and a high level output, respectively, to control switches 337 and 336 to block voltage V and to pass the inverted voltage V respectively. When comparator 320 provides a high level output, the inverted voltage V passes through switch 339 to be used in calculating signal E as previously mentioned, to decrease the acid strength, if other conditions which are hereinafter described are net.

LINEAR PROFIT EQUATION OPERATION Comparators 328A, 329A compare signal E and E respectively, corresponding to differential profit positions p, and p respectively with a ground, corresponding to differential profit position p Comparators 328A, 329A cooperate with AND gate 330A, 331A in the same manner as comparators 328, 329 cooperated with AND gates 330 and 331. AND gates 330A and 331A are enabled, when equation 5 is the controlling equation, by a high level output from an inverter 368 inverting signal E AND gates 330A, 331A are disabled by a low level output from inverter 368 which occurs when alkylation unit is being controlled in accordance with equation 4 so that comparators 328A, 329A have no effect.

For the condition that differential profit position p, is greater than differential profit position p1, Comparator 328A, 329A provide a high level and a low level output, respectively. Comparator 328A output passes through enabled AND gate 330A to render switch 336 conductive while a low level output provided by AND gate 331A in response to comparator 329A output renders switch 337 non-conductive, respectively. The acid strength will then be increased by the amount A as heretofore described. Conversely, when p, is greater than zero, comparators 328A and 329A and AND gates 330A, 331A render switches 336 and 337, respectively, non-conductive and conductive, respectively, so that the acid strength is decreased by the amount A. I

Since switch 338 is rendered non-conductive by the low level of signal E the signal passed by switch 336 or 337 is now passed by another electronic switch 369 which is rendered conductive by a high level output from comparator 328A or 329A passing through an AND gate 330A or 331A and an OR gate 370 to summing means 345.

When position p, is greater than position p, and p comparators 328A, 329A provide low level outputs rendering switch 369 non-conductive. Since switches 339 and 369 are rendered non-conductive, the acid strength will not be changed.

The system of the present invention, as heretofore described, controls an alkylation unit so that the reaction acid in the alkylation unit is at an optimum strength. The reaction acid strength is controlled as a function of the economic values of acid being fed to the alkylation unit and the octane rating of the alkylate produced by the alkylation unitThe control system varies the reaction acid strength under a restrictive condition that the reaction acid strength may not be less than the predetermined level.

What is claimed is:

1. A system for controlling the strength of a reaction acid in an alkylation unit wherein an isoparaffin is reacted with an olefin in the presence of the reaction acid to provide an acid-hydrocarbon mixture to a settler where a hydrocarbon product is separated from the reaction acid and provided to a debutanizer tower whose bottom products include alkylate and a portion of the reaction acid is recycled while the remaining reaction acid is discharged from the alkylation unit and wherein fresh acid is added to the recycled acid to affect the strength of the reaction acid, comprising means for controlling the strength of the reaction acid in accordance with a control signal, means for sensing the flow rates of one of the acid and the bottom products and providing signal representative thereof, means for sensing concentrations of different constituents of the olefin and providing corresponding signals, means for sensing the concentration of the alkylate in the bottom products and providing a signal corresponding thereto, means for sensing the strength A, of the reaction acid and providing a signal corresponding thereto, means for providing signals corresponding to the economic values V A and V of acid and of octane of the alkylate, respectively, and means connected to the sensing means, to the control means and to the value signal means for providing the control signal to the control means in accordance with the signals from the sensing means and the value signal means to achieve an optimum reaction acid strength.

2. A system as described in claim 1 in which the control signal means includes means for providing signals corresponding to an acid strength A greater than the sensed acid strength A to an acid streangth A less than the sensed acid strength A and to a reference acid strength A means connected to the flow rate sensing means, olefin sensing means, to the acid strength sensing means and to the economic value sensing means for providing signals corresponding to anticipated changes p and p in profit associated with the acid strnegths A and A;,, respectively, in accordance with the acid strength A A A and A signals, the acid flow rate signal, the bottoms product flow rate signal, and the economic value signals, and a network connected to the profit change signal means, to the acid strength sensing means, to the control means and to the acid strength signal means for providin g a signal, corresponding to a desired acid strength, to the control means as the control signal in accordance with the acid strength A,, A and A signals and the profit change p and p signals.

3. A system as described in claim 2 in which the profit change signal means includes means connected to the economic value signal means and receiving signals corresponding to octane adder factors 6,, 0 and 0;, to acid rates AR,, AR and AR, and to an alkylate rate ALR for providing the p and p signals in accordance with the economic value signals, the received signals and the following equations:

Pa (#3 1)( 0) i' 2)( A), where 4),, 4;: and 5 are the octane adder factors associated with the sensed acid strength A and the predetermined acid strengths A, and A respectively, and where AR AR and AR;, are the acid rates associated with the sensed acid strength A and the predetermined acid strength A and .4 respectively; rate signal means connected to the flow rate sensing means, to the acid strength sensing means, to the alkylate sensing means, to the acid strength signal means, and to the a -p signal means for providing the ALR, AR AR, and AR;, rate signals to the p -p signal means in accordance with the signals from the flow rate sensing means and the acid strength A A A and A signals; and octane adder factor means connected to the acid strength sensing means, to the acid strength signal means, to the olefin sensing means and to the circuit and receiving direct current voltages corresponding to constants K,, K, and K for providing the octane adder factors (b and (b signals to the circuit in accordance with the sensed acid strength A signal, the olefin constituents signals, the reference acid strength A signal and the received voltages.

4. A system as described in claim 3 in which the rate signal means includes means connected to the flow rate sensing means, to the circuit and receiving direct current voltages corresponding to conversion constants H and J for providing the AR, and the ALR signals in accordance with the sensed acid flow rate FR the sensed bottom products flow rate FR the alkylate concentration ALK signal, the received voltage and the following equations:

AR (H)(FR and ALR (J)(FR )(ALK), acid consumption factor signal means connected to the acid strength sensing means and to the acid strength signal means and receiving the voltages corresponding to the constants K;, K K K and K, for providing acid consumption factor 0 0 and 0 signals in accordance with the sensed acid strength A; signal, the reference acid strength signal A the received voltages and the following equations:

J( a 90) k( a s0) where 0 6 and 0 are acid consumption factors as sociated with the sensed acid strength A and the Y predetermined acid strengths A and A respectively, and means connected to the AR signal means, to the 0 0 and 0 signal means and to the p p signal means for providing the AR and AR signals to the prp signal means in accordance with the AR 0 6 and 0 signals and the following equations:

AR2= AR, and

AR3=AR1.

5. A system as described in claim 4 in which the 4a,, and da signal means includes means connected to the olefin sensing means and receiving a direct current voltage corresponding to the term for providing a ratio M signal in accordance with the olefin constituents signals, the received voltage and the following equation:

M (Propylene/Olefins) X 100 where propylene and olefins refer to their concentrations in the reactions, and a plurality of networks, each netowrk connected to the ratio M signal means, to the acid strength signal means and receiving direct current voltages corresponding to reference ratios Mg and M and constants K, through K one of the networks being connected to the acid strength sensing uses the received voltages and signals to provide an octane factor 4%, d, or dz, signal associated with the acid strength A,, A, or A, signal in accordance with the following equation:

4*. u( oo) b( 90) m) where the term A without a subscript refers to the associated acid strength A, A, or A 4),, corresponds to an octane adder factor (in, d), or dz, when the ratio M signal is equal to or less than the reference ratio M voltage, in accordance with the following equation:

4 v=+ m) I 1 where in, corresponds to an octane adder factor qb 4), or (b, when the ratio M signal is equal to or greater than the reference ratio M voltage, and in accordance with the next two previous equations and the following equation:

where (1),. corresponds to an octane adder factor 42 d, or it, when the ratio M signal is greater than the reference ratio M voltage but less than the reference ratio M voltage.

6. A system as described in claim 5 in which the general profit P equation for the alkylation unit may be a second order equation as follows:

p=Q+RA+SA or a linear equation as follows:

p Q RA where Q, R and S are constants and A is an acid strength, and the control signal network includes means connected to the circuit, to the acid strength signal means and to the acid strength sensing means for providing signals corresponding to R and S in accordance with the acid strength A,, A and A signals, and means connected to the R and S signal means for determining whether the profit equation is a second order equation or a linear equation and providing a signal corresponding to an optimum acid strength A when the profit equation is a second order equation and providing a signal corresponding to a predetermined change A in acid strength when the profit equation is a linear equation and the sensed acid strength A, is not an optimum acid strength.

7. A system as described in claim 6 in which the control means further comprises means connected to the acid strength signal means, to the control means and to the network providing the control signal for permitting the control signal to be provided to the control means when the desired acid strength is equal to or greater than the reference acid strength A and not providing the control signal tothe control means when the desired acid strength is less than the reference acid strength A,,.

8. A system as described in claim 6 in which the R and S signal means provide the R and S signals in accordance with the following equations:

S: [Ps( r a) +Pa( 2"' 1)] and 9. A system as described in claim 6 in which the determining means includes means connected to the R and S signal means for providing the optimum acid strength A, signal in accordance with the R and S signals and the following equation:

A,=-R/2S, change signal means connected to the A, signal means and to the acid strength sensing means for providing a change signal corresponding in magnitude to the difference between the A, and A, signals and in polarity to a relationship between the A, and A signals, first switching means connected to the change signal means and receiving direct current voltages of opposite polarities, one received voltage corresponds to the predetermined change A in one direction while the other voltage corresponds to the predetermined change A in an opposite direction, for providing the one received voltage when the change signal from the change signal means is of one polarity and the other received voltage when the change signal is not of the one polarity, second switching means connected to the first switching means and to the change signal means for passing the change signal while blocking a predetermined change voltage from the first switching means when the change signal has a smaller, or equal, amplitude than a predetermined change voltage, and blocking the change signal from the change signal means while passing a predetermined change voltage from the first switching means when the change signal has a larger amplitude than a predetermined change voltage.

10. A method for controlling the strength of a reaction acid in an alkylation unit wherein an isoparaffin is reacted with an olefin in the presence of the reaction acid to provide an acid-hydrocarbon mixture to a settler where a hydrocarbon product is separated from the reaction acid and provided to a debutanizer tower whose bottom products include alkylate and a portion of the reaction acid is recycled while the remaining reaction acid is discharged from the alkylation unit and wherein fresh acid is added to the recycle acid to affect the strength of the reaction acid, which comprises the following steps:

controlling the strength of the reaction acid in accordance with a control signal, sensing the flow rates of the reaction acid and the bottom products, providing signals corresponding to the sensed flow rates, sensing the concentrations of different constituents of the olefin, providing signals corresponding to the sensed concentrations of constituents of the olefin, sensing the concentration of alkylate in the bottom products, providing a signal corresponding to the sensed alkylate concentration, sensing the strength'A, of the reaction acid, providing a signal corresponding to the sensed acid strength, providing signals corresponding to the economic values V, and V, of the acid and of octane rating of the alkylate, respectively, and providing the control signal in accordance with the signals corresponding to the sensed flow rate, the sensed acid strength, the sensed constituent concentrations and the economic value signals.

11. A method as described in claim 10 in which the providing of the control signal step includes the steps of providing signals corresponding to an acid strength A, greater than the sensed acid strength A to an acid strength A, less than the sensed acid strength A and to a reference acid strength A providing signals cor 

1. A system for controlling the strength of a reaction acid in an alkylation unit whErein an isoparaffin is reacted with an olefin in the presence of the reaction acid to provide an acidhydrocarbon mixture to a settler where a hydrocarbon product is separated from the reaction acid and provided to a debutanizer tower whose bottom products include alkylate and a portion of the reaction acid is recycled while the remaining reaction acid is discharged from the alkylation unit and wherein fresh acid is added to the recycled acid to affect the strength of the reaction acid, comprising means for controlling the strength of the reaction acid in accordance with a control signal, means for sensing the flow rates of one of the acid and the bottom products and providing signal representative thereof, means for sensing concentrations of different constituents of the olefin and providing corresponding signals, means for sensing the concentration of the alkylate in the bottom products and providing a signal corresponding thereto, means for sensing the strength A1 of the reaction acid and providing a signal corresponding thereto, means for providing signals corresponding to the economic values VA and VO of acid and of octane of the alkylate, respectively, and means connected to the sensing means, to the control means and to the value signal means for providing the control signal to the control means in accordance with the signals from the sensing means and the value signal means to achieve an optimum reaction acid strength.
 2. A system as described in claim 1 in which the control signal means includes means for providing signals corresponding to an acid strength A2 greater than the sensed acid strength A1, to an acid strength A3 less than the sensed acid strength A1, and to a reference acid strength A90; means connected to the flow rate sensing means, olefin sensing means, to the acid strength sensing means and to the economic value sensing means for providing signals corresponding to anticipated changes p2 and p3 in profit associated with the acid strnegths A2 and A3, respectively, in accordance with the acid strength A1, A2, A3 and A90 signals, the acid flow rate signal, the bottoms product flow rate signal, and the economic value signals, and a network connected to the profit change signal means, to the acid strength sensing means, to the control means and to the acid strength signal means for providing a signal, corresponding to a desired acid strength, to the control means as the control signal in accordance with the acid strength A1, A2 and A3 signals and the profit change p2 and p3 signals.
 3. A system as described in claim 2 in which the profit change signal means includes means connected to the economic value signal means and receiving signals corresponding to octane adder factors theta 1, theta 2 and theta 3, to acid rates AR1, AR2 and AR3 and to an alkylate rate ALR for providing the p2 and p3 signals in accordance with the economic value signals, the received signals and the following equations: p2 ( phi 2 - phi 1)(ALR)(VO) - (AR1- AR2)(VA) and p3 ( phi 3 - phi 1)(ALR)(VO) - (AR1- AR2)(VA), where phi 1, phi 2 and phi 3 are the octane adder factors associated with the sensed acid strength A1 and the predetermined acid strengths A2 and A3, respectively, and where AR1, AR2 and AR3 are the acid rates associated with the sensed acid strength A1 and the predetermined acid strength A2 and A3, respectively; rate signal means connected to the flow rate sensing means, to the acid strength sensing means, to the aLkylate sensing means, to the acid strength signal means, and to the p2- p3 signal means for providing the ALR, AR1, AR2 and AR3 rate signals to the p2-p3 signal means in accordance with the signals from the flow rate sensing means and the acid strength A1, A2, A3 and A90 signals; and octane adder factor means connected to the acid strength sensing means, to the acid strength signal means, to the olefin sensing means and to the circuit and receiving direct current voltages corresponding to constants Kf, Kg and Kh for providing the octane adder factors phi 1, phi 2 and phi 3 signals to the circuit in accordance with the sensed acid strength A1 signal, the olefin constituents signals, the reference acid strength A90 signal and the received voltages.
 4. A system as described in claim 3 in which the rate signal means includes means connected to the flow rate sensing means, to the circuit and receiving direct current voltages corresponding to conversion constants H and J for providing the AR1 and the ALR signals in accordance with the sensed acid flow rate FRA, the sensed bottom products flow rate FRp, the alkylate concentration ALK signal, the received voltage and the following equations: AR1 (H)(FRA) and ALR (J)(FRBP)(ALK), acid consumption factor signal means connected to the acid strength sensing means and to the acid strength signal means and receiving the voltages corresponding to the constants Kf, Kg. Kh, Ki and Kj for providing acid consumption factor theta 1, theta 2 and theta 3 signals in accordance with the sensed acid strength A1 signal, the reference acid strength signal A90, the received voltages and the following equations: theta 1 Kf+ Kg(A1- A90)+Kh(A1- A90)2+ Ki(A1- A90)+Kj(A1-A90)4+ Kk(A1- A90)5 theta 2 Kf+ Kg(A2- A90)+Kh(A2- A90)2+ Ki(A2- A90)3+ Kj(A2-A90)4+ Kk(A2- A90)5 theta 3 Kf+ Kg(A3- A90)+Kh(A3- A90)2+ Ki(A3- A90)3+ Kj(A3-A90)4+ Kk(A3- A90)5 where theta 1, theta 2 and theta 3 are acid consumption factors associated with the sensed acid strength A1 and the predetermined acid strengths A2 and A3, respectively, and means connected to the AR1 signal means, to the theta 1, theta 2 and theta 3 signal means and to the p2- p3 signal means for providing the AR2 and AR3 signals to the p2- p3 signal means in accordance with the AR1, theta 1, theta 2 and theta 3 signals and the following equations: AR2 ( theta 2/ theta 1) AR1, and AR3 ( theta 3/ theta 1) AR1.
 5. A system as described in claim 4 in which the phi 1, phi 2 and phi 3 signal means includes means connected to the olefin sensing means and receiving a direct current voltage corresponding to the term 100 for providing a ratio M signal in accordance with the olefin constituents signals, the received voltage and the following equation: M (Propylene/Olefins) X 100 where propylene and olefins refer to their concentrations in the reaction, and a plurality of networks, each netowrk connected to the ratio M signal means, to the acid strength signal means and receiving direct current voltages corresponding to reference ratios MU and ML and constants Ka through Kd, one of the networks being connected to the acid strength sensing means, uses the received voltages and signals to provide an octane factor phi 1, phi 2 or phi 3 signal associated with the acid strength A1, A2 or A3 signal in accordance with the following equation: phi L Ka(A-A90) + Kb(A-A90)2 + Kc(A-A90)5, where the term A without a subscript refers to the associated acid strength A1, A2 or A3, phi L corresponds to an octane adder factor phi 1, phi 2 or phi 3 when the ratio M signal is equal to or less than the reference ratio ML voltage, in accordance with the following equation: phi U + Kd(A-A90)3 where phi U corresponds to an octane adder factor phi 1, phi 2 or phi 3 when the ratio M signal is equal to or greater than the reference ratio MU voltage, and in accordance with the next two previous equations and the following equation: phi L U phi L(MU - M/MU - ML) + phi U(M - ML/MU - ML) where phi L U corresponds to an octane adder factor phi 1, phi 2 or phi 3 when the ratio M signal is greater than the reference ratio ML voltage but less than the reference ratio MU voltage.
 6. A system as described in claim 5 in which the general profit P equation for the alkylation unit may be a second order equation as follows: p Q + RA + SA2, or a linear equation as follows: p Q + RA where Q, R and S are constants and A is an acid strength, and the control signal network includes means connected to the circuit, to the acid strength signal means and to the acid strength sensing means for providing signals corresponding to R and S in accordance with the acid strength A1, A2 and A3 signals, and means connected to the R and S signal means for determining whether the profit equation is a second order equation or a linear equation and providing a signal corresponding to an optimum acid strength AO when the profit equation is a second order equation and providing a signal corresponding to a predetermined change Delta in acid strength when the profit equation is a linear equation and the sensed acid strength A1 is not an optimum acid strength.
 7. A system as described in claim 6 in which the control means further comprises means connected to the acid strength signal means, to the control means and to the network providing the control signal for permitting the control signal to be provided to the control means when the desired acid strength is equal to or greater than the reference acid strength A90 and not providing the control signal to the control means when the desired acid strength is less than the reference acid strength A90.
 8. A system as described in claim 6 in which the R and S signal means provide the R and S signals in accordance with the following equations: R ( p2(A32- A12) + p3(A12- A22))/D, S ( p2(A1- A3) + p3(A2- A1))/D, and D A1(A22- A32) + A2(A32- A12) + A3(A12- A22).
 9. A system as described in claim 6 in which the determining means includes means connected to the R and S signal means for providing the optimum acid strength Ao signal in accordance with the R and S signals and the following equation: Ao - R/2S, change signal means connected to the Ao signal means and to the acid strength sensing means for providing a change signal corresponding in magnitude to the difference between the Ao and A1 signals and in polarity to a relationship between the Ao and A1 signals, first switching means connected to the change signal means and receiving direct current voltages of opposite polarities, one received voltage corresponds to the predetermined change Delta in one direction while the other voltage corresponds to the predetermined change Delta in an opposite direction, for providing the one received voltage when the change signal from the change signal means is of one polarity and the other received voltage when the change signal is not of the one polarity, second switching means connected to the first switching means and to the change signal means for passing the change signal while blocking a predetermined change voltage from the first switching means when the change signal has a smaller, or equal, amplitude than a predetermined change voltage, and blocking the change signal from the change signal means while passing a predetermined change voltage from the first switching means when the change signal has a larger amplitude than a predetermined change voltage.
 10. A method for controlling the strength of a reaction acid in an alkylation unit wherein an isoparaffin is reacted with an olefin in the presence of the reaction acid to provide an acid-hydrocarbon mixture to a settler where a hydrocarbon product is separated from the reaction acid and provided to a debutanizer tower whose bottom products include alkylate and a portion of the reaction acid is recycled while the remaining reaction acid is discharged from the alkylation unit and wherein fresh acid is added to the recycle acid to affect the strength of the reaction acid, which comprises the following steps: controlling the strength of the reaction acid in accordance with a control signal, sensing the flow rates of the reaction acid and the bottom products, providing signals corresponding to the sensed flow rates, sensing the concentrations of different constituents of the olefin, providing signals corresponding to the sensed concentrations of constituents of the olefin, sensing the concentration of alkylate in the bottom products, providing a signal corresponding to the sensed alkylate concentration, sensing the strength A1 of the reaction acid, providing a signal corresponding to the sensed acid strength, providing signals corresponding to the economic values VA and VO of the acid and of octane rating of the alkylate, respectively, and providing the control signal in accordance with the signals corresponding to the sensed flow rate, the sensed acid strength, the sensed constituent concentrations and the economic value signals.
 11. A method as described in claim 10 in which the providing of the control signal step includes the steps of providing signals corresponding to an acid strength A2 greater than the sensed acid strength A1, to an acid strength A3 less than the sensed acid strength A1 and to a reference acid strength A90; providing signals corresponding to anticipated changes p2 and p3 in profit associated with the acid strengths A2 and A3, respectively, in accordance with the acid strength A1, A2, A3 and A90 signals, the aCid flow rate signal, the bottom product flow rate signal, and the economic value signals; and providing a signal corresponding to a desired acid strength as the control signal in accordance with the acid strength A1, A2 and A3 signals and the profit change p2 and p3 signals.
 12. A method as described in claim 11 in which the providing of the profit change signal steps includes the steps of providing signals corresponding to octane adder factors phi 1, phi 2 and phi 3 in accordance with the sensed acid strength A1 signal, the reference acid strength A90 signal, the olefin constituents signals; providing rate signals ALR, AR1, AR2 and AR3 corresponding to an alkylate rate, an acid rate associated with acid strength A1, an acid rate associated with acid strength A2 and an acid rate associated with acid strength A3, respectively, in accordance with the flow rate signals, the alkylate concentration signal and the acid strength A1, A2, A3 and A90 signals, and providing the p2 and p3 signals in accordance with the economic value signals, the octane adder factors phi 1, phi 2 and phi 3 signals, the ALR signal and the AR1, AR2 and AR3 signals in the following equations: p2 ( phi 2 - phi 1)(ALR)(VO) - (AR1- AR2)(VA) and p3 ( phi 3 - phi 1)(ALR)(VO) - (AR1-AR2)(VA).
 13. A method as described in claim 12 in which the step of providing rate signals includes providing the AR1 rate signal and the ALR rate signal in accordance with the signal corresponding to the flow rate FRA of the acid and the signal corresponding to the flow rate FRBP of the sensed bottom product and the signal corresponding to the alkylate ALK concentration and the following equations: AR1 (H)(FRA) and ALR (J)(FRBP)(ALK) where H and J are conversion factors, providing acid consumption factor theta 1, theta 2 and theta 3 signals associated with the acid strength A1, A2 and A3 in accordance with the sensed acid strength A1 signal, the reference acid strength A90 signal and the acid strength signals A2 and A3 and the following equations: theta 1 Kf+Kg(A1-A90)+Kh(A1-A90)2+Ki(A1-A90)3+Kj(A1-A90)4 + Kk(A1-A90)5 theta 2 Kf+Kg(A2-A90)+Kh(A2-A90)2+Ki(A2-A90)3+Kj(A2-A90)4+Kk(A2-A90)5 theta 3 * Kf+Kg(A3-A90)+Kh(A3-A90)2+Ki(A3-A90)3+Kj(A3-A90)4 +Kk(A3-A90)5 where Kf, Kg, Kh, Ki, Kk and Kj are constants, and providing the AR2 and AR3 rate signals in accordance with the AR1 rate signals and the acid consumption factor theta 1, theta 2 and theta 3 signals and the following equations: AR2 ( theta 2/ theta 1) AR1, and AR3 ( theta 3/ theta 1) AR1
 14. A mEthod as described in claim 12 in which the step of providing the phi 1, phi 2 and phi 3 signals include providing a ratio M signal in accordance with the olefin constituent signals and the following equation: M (Propylene/Olefins) X 100 where propylene and olefins refer to their concentrations, and in which each phi 1, phi 2 or phi 3 signal is provided in accordance with the associated acid strength A1, A2 or A3 signal and the reference acid strength signal A90 and the following equation: phi L Ka(A-A90) + Kb(A-A90)2+Kc(A-A90)5, where the term A without a subscript refers to the acid strength A1, A2 or A3 signal other than the reference acid strength when the ratio M signal is equal to or less than a reference ratio ML signal, in accordance with the following equation: phi U +Kd(A-A90)3 where the ratio M signal is equal to or greater than the reference ratio MU signal, and in accordance with the following equation: phi L U phi L(MU - M/MU - ML) + phi u (M - ML/MU -ML) where phi L u corresponds to an octane adder factor phi 1, phi 2 or phi 3 when the ratio M signal is greater than the reference ratio ML voltage but less than the reference ratio MU voltage. 